A percolation has a few advantages and disadvantages compared to a maceration. A Percolation is much faster, taking only about 2 days to the finished tincture, while a maceration can take several weeks. A percolation also ends up with a more potent medicine as a standard maceration because the herbs are ground to a powder, which leaves them with a much higher surface area. If a maceration would be done with ground herbs and regularly stirred the medicine might be of the same potency?
Disadvantages of a percolation are that it needs dried herbs, so fresh herbs are not possible and a herb grinder is needed to grind the herbs. Some herbs are very hard to grind and are therefor rather used in a maceration. Also a glass-cutter might be needed to make a percolation flask out of a bottle.
The powder for the herbs should not be too coarse as the alcohol will just rush through it and also not too fine as it can get easily overcompacted and the alcohol will get stuck.
One day before the percolation is started the ground herbs are pre-moistened with a 50 % alcohol and 50 % water mixture until the texture is like a cookie-dough, holding together by itself but breaking apart between the fingers. Some single herbs require different alcohol ratios but if you have a herb formula and no other indication you would go for a 50 % ratio as standard.
Before the herbs go into the percolation flask, the lid should be on and a cotton ball is put to the bottom to prevent the herbs from falling out once the lid gets removed.
Then the herbs are added and lightly tamped down with a stick that has a flat end after every other table spoon of herbs added. Try to keep the surface of the herbs flat all the time and don't overcompact them. Also look from the side to see if any air pockets are forming.
Once all the herbs are in the percolation flask (the one in the back holds 100 g, the one in the front 50 g) a coffee filter is added to the top to prevent the herbs from getting into turbulence once the alcohol is added.
The next step is to remove the lid! This step gets easily overlooked but is very important. If the lid is not removed before the alcohol is added, air will have only the way through the herbs to make room for the alcohol and will drive holes into the nicely packed herbs. After the lid is removed the alcohol is added to the top. Look if it is running homogenously on all sides through the ground herbs. If it is slower or faster on one side this indicates over- oder underpacking. Make sure that the alcohol does not run out on the top or air will get back into the herbs. Once the alcohol reaches the cotton ball and starts dripping, close the lid. The percolation could be run right now, but it does not harm to let it saturate with the alcohol for another few hours or even a day if hard roots are included before opening the lid again.
Open the lid just a bit so that there is about 1 to 2 drips per second. Make sure that the alcohol is never running out on the top. Normally you would go for a 1:5 ratio by yield, meaning for 100 g of herbs you add alcohol until you get 500 ml of tincture in the jar. As the herbs soak a bit of the alcohol you will end up putting in more than 500 ml. If you want a more potent tincture, you could go for a 1:4 ratio.